Indicator light for Brita filter not working

it may take a few minutes to purge air from system, open ro fausct and let it bleed air and run water with spurts.

https://www.youtube.com/watch?v=-guPFrVEbgM

refer to instruction.
Move the filter handle toward you to activate the filtered water

https://www.aquasana.com/info/education/time-for-a-filter-change

How do you reset a Brita filter indicator?

1. Press the Reset button firmly for 5 seconds. If needed, use a capped ballpoint pen.
2. The green, yellow and red lights will simultaneously blink.
3. Release the RESET button when only the green light blinks.

Take it to Walmart and exchange it for another one even if you didn't buy it there

When you initially soak the bag in water make sure to squeeze it lightly and shake to release all the air bubbles. Also, you should pour out the first couple pitchers of water after using a new filter as it takes time to break in. This way all of the gray or black filter water will be gone by the time you wish to drink. For more water filter and pitchers go to www.freshwatersystems.com.

It sounds like the adapter was screwed in at an angle. This causes the threads to cross in turn making it near impossible to unscrew. Since it is plastic I recommend buying a new adapter. I know it's unfortunate, however it is a lost cause.

I have a Brita faucet filter (model FF-100) that lately has become harder and harder to turn. I toyed with the idea of forcing the unit apart but, instead opted to lube the mechanism directly from the top, where the unit attaches to the faucet.
To this mean, you will have to 1) Detach the unit from the faucet. 2) Remove the filter. 3) Thoroughly wash the unit, inside and out, turning the knob to flush any debris that may be present. 4) Pour some drops of vegetable oil inside the mounting opening, coating the valve stem within. (Oil may pass thru the unfiltered water outlet, so choose an appropriate working space). 5) Turn the water handle (knob) to lube the valve repeatedly, until it loosens. 5.b) Optionally, you could let the oil sit for some time inside the base. 6) Rinse the unit and reinstall it on faucet (without the filter). 7) Turn knob to unfiltered position, and flush with warm/hot water. 8) Do likewise with knob set to filtered, but open faucet only slightly, to avoid over-spraying. 9) Remove base unit from faucet and repeat steps 3-9, as needed. 10) Reinstall unit with filter, as instructed by manual.
Water valves may seize due to mineral deposits. While you may be tempted to use detergents or solvents, be reminded that unless thoroughly rinsed, chemicals may corrode plastics, degrade your filter, or even wind up in your drinking water, so caveat.

The LED monitor should light up as Green when the membrane is producing the proper water quality (80%+ TDS rejection). If the LED light stays Red this indicates the RO membrane is bad, all the filters (including membrane) should be changed and system sanitized. The batteries in the TDS monitor should be changed yearly also. Don't have a lot of faith in that indicator light. The best way to test for TDS rejection is with a digital TDS meter which indicates the amount of rejection. Compare the incoming water to the product water of the RO.
RJ

Want a free adapter and patient enough to wait for a couple of weeks to get them?
"To receive a special adapter free of charge, call 1-800-24-BRITA or 1-800-387-6940 (CANADA)."
Call the number above and a voice prompt will give you instructions on how to get your adapter for free. 2 weeks might be too long but the best thing is it is made of stainless steel/chrome and it comes in 3 different kind of adapters with rubber washers.